Measurement of one's visual field is important for a variety of reasons including the diagnosis of glaucoma as well as other human visual system diseases or impairments. In general, the prior techniques for determining one's visual field and any blind spots have been quite slow and tedious and require a definite subjective response from the person being tested in order to determine whether he has sighted the target at a particular location in his visual field. Additionally, the previously employed tests require administration by one having relatively high degree of skill such as an ophthalmic technician, optometrist or ophthalmologist. For example, in the most common type of visual field test, a hand held target such as a small disc at the end of a wand, is moved about the subject's visual field by the examiner while the subject fixates on a central point. During movement of the hand held target through the subject's field, the examiner asks the subject repeatedly whether he can see the movable target as it is passing from location to location. The examiner may plot, manually, the location of each point which is seen by the subject, or alternatively, he may plot those locations which the subject is unable to see, and which, therefore, define his blind spot.
In order to overcome the uncertainties and difficulties in the foregoing testing techniques some attempts have been made to automate partly the foregoing visual field test, such as employing an arrangement for automatically presenting a series of targets to the subject. Although these devices are somewhat faster than the completely manual test described above, they still are relatively slow and require that the subject respond consciously and intentionally when he sees the target. For example, the response may be verbal or may be indicated by the subjective manipulation of a lever or a button.
Also among the primary difficulties in obtaining fast and accurate plots of the subject's visual field is that the examiner must be assured that the subject's line of sight is directed toward a central fixation point or other known reference point before the target is presented to him. In some instances this may be quite difficult when problems of communication exist between the subject and the examiner as, for example, when testing the young, the aged, or persons whose native language is different than that of the examiner. Furthermore, any such difficulties render efficient and accurate testing still more complicated because it may confuse the results of the test.
A further difficulty in conducting visual field tests with prior techniques is that an indication by the subject that he has seen the target may be the result of hunting eye movements in which, he did not at first actually see the target but moved his eyes about slightly, in a searching motion, and then having seen the target, then moved his eyes directly to it. The present invention employs means for discriminating between such hunting movements and movements in which the presented target was initially seen by the subject.
It is among the primary objects of the invention to provide an apparatus for determining a subject's visual field which avoids the foregoing and other difficulties.